The traditional style of windows used in the United States, and many other places that had been colonized by the English, is the single-hung and the double-hung sash window. A Double-hung window assembly typically comprises two sash windows each of which slide vertically in a master frame. To enable a user to easily open or close such windows, as well as to enable the window to remain static once it has been opened or closed, a balance assembly is attached to each window. Such balance assemblies were originally just counterweights on either side of the window, where the weights were suspended by a cord or chain across a pulley and attached to the sash window.
Advances in window construction have been significant, and although contemporary windows may visually resemble their ancestor described above, a resemblance which may even permit its use as a replacement window in historic homes, the technological improvements render them very different as to the materials used, and vastly superior in terms of performance. Many of the changes have been due in part to the demand for greater energy efficiency in both hotter and colder climates, where the savings attributable to reductions in the corresponding air-conditioning or heating expenses can be considerable.
Increases in thermal efficiency have been made through the use of an Insulating Glass Unit (IGU) or double-paned window, in which two panes of glass are hermetically sealed to form a single glazed unit, with an ‘air-space’ between the two panes of glass. This arrangement, also known as “double-glazing,” generally reduced or eliminated the problem of windows fogging or frosting, and of the windows being uncomfortably cold upon contact. Further improvement were made by filling the ‘air-space’ with inert gases, such as argon and krypton, both of which have a higher resistance to heat flow than does air. Additional thermal resistance of an IGU has also been achieved through the use of low-emissivity coatings, which are typically applied to the non-exposed, interior side of the glass pane or panes. The coatings can be alternatively designed for a high or low solar heat gain coefficient (SHGC), depending on the location's requirements, while simultaneously reducing the window's u-factor, or rate at which the unit conducts infrared radiation (non-solar heat) from a warm pane of glass to a cooler pane of glass.
Despite these tremendous advances, a further consideration as to the overall energy efficiency of a window is that the window's frame constitutes roughly 25% of its area, making its conductivity a substantial factor in the window's energy performance. Wood frame windows are still widely available, however, the maintenance drawbacks of solid wood windows has led to some of the material upgrades previously mentioned, as frames have become available in the form of vinyl-clad and aluminum-clad wood, and such frames actually comprise a major share of the market. Not surprisingly, the market for energy conductive aluminum frame windows is relatively small. But a large intermediate share is held by insulated vinyl and insulated fiberglass frame windows which are among the best energy performers.
Advances have similarly been made in the associated window hardware, including the latch which enables a sash window to not only move vertically, but to pivot inwardly as well. One such latch is shown by U.S. Pat. No. 5,139,291 to Schultz. The latch is adapted for installation into a window having a hallow top sash rail. The latch housing has a “side wall rail,” which, in combination with the housing cover edge, forms a groove, where the groove cooperates with the edge of the top wall of the top sash rail to retain the latch. The latch slides into a side opening in the sash window stile, which has a periphery to match the latch profile. A tab on the front face of the latch engages the stile to retain the tilt latch in position.
However, many if not most coastal areas now mandate that the windows installed be constructed to satisfy very stringent standards. These standard may include a requirement that the window be able to structurally withstand, for a set period of time, a specified design pressure, which would permit the window to maintain its integrity throughout the sustained winds of a category five hurricane. Under such loading, it is not uncommon to see a window convex a couple of inches, but when properly designed, the window will regain its original form. This significant deformation under such high wind loads creates as serious if not fatal problem for the hardware currently available, particularly the tilt latch. The Schultz tilt latch would not be retained by the sash rail as described above, when the window experienced high wind loading and deformation, especially in the case of a vinyl frame window, which lacks the structural rigidity of the energy inefficient aluminum frame window.
It is possible to utilize the top plate of the latch to restore some of the frame's structural rigidity, and may be accomplished in the approach shown in FIG. 3 of U.S. Pat. No. 7,069,694 to Fullick. The top plate in Fullick widens to permit the installation of mechanical fasteners which connect the top plate to the opposite sides of the top wall of the top rail. Although this approach would help to limit the local window frame deformation which would impair the integrity of the latch installation during loading and deformation occurring in extreme weather conditions, it requires additional parts and manufacturing operations not needed with the Schultz configuration. The Fullick design also affects the aesthetic appearance of the latch, which is a significant factor in a competitive market where such a tradeoff, for the most part, may not enhance overall value to the consumer because statistically speaking, the ability of the latch to satisfy high wind loading conditions of extreme weather phenomena will seldom be utilized.
Also, the latch in U.S. Pat. No. 5,671,958 to Szapucki has resilient tabs 18, 18′, 20, and 20′, as shown in its FIG. 12, which permit a drop down latch installation into the top rail of the window, rather than an installation endwise through an opening in the stile. These tabs in Szapucki are designed to be resilient so that they snap outwardly under the edges of the top plate. The tabs may assist in keeping the latch in place while the window experiences some minor deformation associated with ordinary use and loading, but the tabs are extremely limited by their design and inherent ability to withstand large scale deformations that accompany the high wind loading conditions.
The invention disclosed herein provides a more advanced and unique concept for installation than provided by Schultz, and without the inherent drawbacks created by incorporation of the Fullick top plate and fasteners. This invention furthermore overcomes the limitations posed by attempting to use other existing designs represented by the Szapucki patent.